الفهرس 
AcknowledgmentOnly 14 pages are availabe for public view
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Abstract
The tllermal expansion is an important property characterizing semicrystalline polymers when used or processed. The molecular composite model is found to be a simple , safe and accurate model for the prediction of the mechanical
and the therma 1 properties for various
semicrystalline polymers. It was successfully used for the
prediction of stiffness, strength, and thermal expansion of polyethylene and stiffness and strength of polypropylene Po lyoxymethylene is considered one of the best engineering plastics. This study is an attempt to apply the
molecular composite model on isotropic polyoxymethylene sheets for the prediction of their thermal epansivity . In this model , the semicrystalline polyoxymethylenesheet isconsidered to behave as a two phase composite material composed of a crystalline phase embedded in an amorphous phase. The sheet is modeled as a quasi-isotropic laminate
formed of stacked oriented laminae, each of them is composed of anisotropic reinforcements (crystalli tes of
knownorientation embedded in an isotropic unoriented matrix
(amorphous region). The properties of each lamina are determined first followed by those of the overall stack.
Also the model is used to investigate the variation of the thermal expansion
coefficient ofisotropicpolY0XYmet.hylene with some morphological and st.ructural